The present invention is directed to an improvement in gate valves which prevents undesired and potentially distructive pressure build up within the gate housing. The invention is particularly suited for above-ground petroleum pipelines and for use in environments subject to extreme temperature fluctuations.
Prior art gate valves for use in cutting off flow in a petroleum line, as shown for example in Baugh U.S. Pat. No. 3,768,774, include a housing which extends both above and below the pipeline. Within the housing is a valve gate having an opening which is aligned with the interior of the pipeline when the gate valve is in its fully opened position. The gate is guided, normally, by the interior surfaces of the gate housing and is movable by means of a hand wheel and jack screw arrangement.
A typical cause of failure of such prior art valves is the expansion of oil trapped within the gate housing as a result of temperature changes, which expansion can cause greatly increased internal pressure when the gate valve is in its closed position, with the gate faces blocking the pipe in both directions from the gate.